These studies are generally concerned with the role of diaphragm and chest wall afferent neural information in the control of respiration. It has been shown that they are involved in the control of respiratory muscle activity at the spinal level. Very little experimental data is available, however, concerning afferent information from respiratory muscle mechanoreceptors ascending to supra-spinal levels and the role this information may have in central respiratory control. The first objective is to answer the question of whether afferent pathways exist from the diaphragm to the central respiratory centers; this will be answered by monitoring the effects on medullary respiratory neurone activity of electrically stimulating phrenic nerve afferents. Second and third objectives are to determine if afferent information from the diaphragm (if pathways exist) and chest wall has an active role in the central control of respiration during normal breathing. These objectives will be approached by systematically sectioning the appropriate afferent pathways, respectively, thoracic dorsal roots (T1-T12) and cervical dorsal roots (C4-C7). The effect of these sections on tidal volume and respiratory rate will be monitored as an indicator of central respiratory activity. The fourth and fifth objectives are to investigate the roles of diaphragm (if pathways exist) and chest wall afferents in the central adjustments of tidal volume and respiratory rate following mechanical loading of respiration. The effects on respiratory pattern of adding elastic and resistive loads to respiration will be monitored with and without the appropriate afferent pathways (described above). BIBLIOGRAPHIC REFERENCES: Shannon, R. (1975). Respiratory frequency control during external elastic loading and chest compression. Respir. Physiol. 23: 11-22. Shannon, R. (1975). Effects of thoracic dorsal rhizotomies on the respiratory pattern in anesthetized cats. The Physiologist 18: 386.